Machine-Type Communication (MTC) is a form of data communication which involves one or more entities that do not necessarily need human interaction. MTC is an important and growing revenue stream for wireless network operators. MTC devices, such as monitors, sensors, controls, etc., may also be referred to as MTC user equipment (MTC UE). Operators benefit from serving MTC devices with already deployed radio access technology. For example, Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) is a competitive radio access technology for efficient support of MTC.
Lower cost MTC devices facilitate and expedite implementation of the concept known as the “internet of things”. In many applications, MTC devices may require low operational power consumption and may communicate with infrequent and short-duration burst transmissions. In addition, MTC devices deployed deep inside buildings may require coverage enhancement in comparison to a defined LTE cell coverage footprint.
3GPP LTE Rel-12 has defined an MTC UE power saving mode that facilitates longer battery life and a new MTC UE category that facilitates reduced modem complexity. Work in Rel-13 is expected to further reduce UE cost and provide coverage enhancement.
For operators to serve MTC devices within a deployed radio access network, such as an LTE network, the MTC devices share the uplink and downlink channels available in the network with traditional UEs such as smartphones, tablets, etc. In an LTE system the available uplink and downlink channels may be described in frequency domain by certain bandwidth or sub-channels and in the time domain by certain subframes. Portions of the available bandwidth and subframes may be allocated for transmission of control information, for user data, or both.
For example, downlink transmissions may be dynamically scheduled. In each subframe a base station may transmit control information about which wireless device may transmit on which resources. The downlink control information may be carried by the physical downlink control channel (PDCCH). Uplink data transmissions may also be dynamically scheduled using the PDCCH. Unlike in downlink, however, traditional uplink data transmission occurs in a predefined number of subframes after the PDCCH. The uplink channel carrying the uplink data may be referred to as the Physical Uplink Shared Channel (PUSCH). A wireless device may also transmit channel quality information in the uplink.
Sounding Reference Symbol (SRS) is a type of uplink transmission used for measuring signal quality. A wireless device transmits an SRS signal to a base station at a particular frequency during a particular subframe. The base station receives the SRS and determines a quality associated with the received signal. The base station may make scheduling and/or resource allocation decisions based on the determined signal quality. SRS is traditionally transmitted in particular subframes. Like other parameters in LTE, resources used for SRS transmission may be signaled to a wireless device from a base station.
MTC devices may include optimizations to facilitate energy efficient operation and relatively low cost of manufacturing. MTC devices also co-exists with traditional UEs in the existing framework of an operators wireless network. To co-exist, MTC devices may share the uplink and downlink resources of the wireless network.